ESTABLISHING THE HATCHERY 



laying out the dam and outlining 

 the confines of the water level in the 

 pond. Because of the acreages of 

 water impounded, earthen dams are 

 used almost exclusively. Deter- 

 mining the desirable top width is 

 the first step in the design of the 

 dam. Generally, the top of the dam 

 is 8 feet wide, but if it is to be used 

 as a road for automobile travel, it 

 should be at least 11 feet wide. The 

 equipment to be used in construct- 

 ing the dam also influences the 

 width of the top. If teams are used, 

 the top of the dam should be 5 feet 

 wide ; if tractors, a width of at least 

 10 feet is required. When the 

 height of the dam and width of the 

 top are determined, the base can be 

 laid out. 



Ordinarily, the upstream, or 

 pond, side of the dam is sloped at 

 tlie rate of 3 feet for each 1 foot of 

 height. On the downstream side, 

 the slope is generally 2 to 1. If the 

 soil contains more than the recom- 

 mended amount of sand or gravel, 

 however, the slope should be in- 

 creased to as much as 5 to 1, de- 

 pending on the nature of the con- 

 struction materials used. This 

 simply means that if the top of the 

 dam is 8 feet wide and the height is 

 10 feet, the base will be 78 feet wnde. 



Tlie site of the crest of the dam 

 should be laid out first, then stakes 

 set along the inside and outside toes, 

 or limits, of the dam. Stakes 

 should also indicate the limits of 

 the water level in the pond. The 

 dam should be high enough-to allow 

 2 to 8 feet of freeboard ; that is, the 

 top should be 2 or 8 feet above the 



normal water level of the pond 

 (fig. 5). 



All trees and bushes should then 

 be removed from the dam site or 

 stacked and burned. All stumps 

 sliould be removed from the pond 

 site, particularly if the pond is to 

 be drained for the removal of min- 

 nows, in which case it is also desira- 

 ble to grade the bottom so that no 

 low spots or water pockets will be 

 left after the pond has been drained. 

 Every piece of root or stump should 

 be removed from the site where the 

 dam is to be located. If this is not 

 done, the decaying wood may cause 

 trouble. 



The next step in construction of 

 the dam is to form a tight bond be- 

 tween the dam and the base on 

 which the dam rests. If the surface 

 is covered with a layer of organic 

 matter, it should be removed and 

 stored for later use in covering sec- 

 tions of the dam which will be 

 seeded with vegetation. The area 

 covered by the base of the dam 

 should then be plow'ed. 



No structure is better than its 

 foundation. To assure a good pond, 

 a section of earth should be re- 

 moved, parallel to and directly un- 

 der what will be the highest part of 

 (he dam, down to solid, mineral soil. 

 If clay soils are underlaid witli 

 sand or gravel, do not dig through 

 the clay into the sand, or the pond 

 will leak. Excavation for the clay 

 core may be accomplished with 

 ('(piipment commonly used, but un- 

 der certain conditions may he done 

 more rapidly with dynamite. 

 Dynamite is particularly efl'ective 



10 



